LASER TRIM CONTROL OF OSCILLATOR TEMPERATURE COMPENShTION
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-02
An inherent problem in crystal oscillators is that the frequency will vary as a function oftemperature. One way to reduce this variation to an acceptable level is to use some sort of temperature compensa- tion scheme. In some applications the compensa- tion can be accomplished by the use of a TC cap in the oscillator circuit. The capacitance of a TC cap by definition will vary as a mnction of temperature. TC caps are available with various slopes. For exam- ple an NlOOO TC cap has a slope of- 1000 ppm/"C, while a P300 has a slope of +300 ppm/"C, and an NPO has a slope of 0 ppm/"C. Thus if a crystal were mated with a TC cap of the appropriate slope and installed in an oscillator, the temperature induced change in oscillator Frequency due to the crystal and the temperature induced change in oscillator fre- quency due to the TC cap will tend to negate each other. The end result is a more temperature stable oscillator.